This application is based on and claims priority to Japanese Patent Application No. 2001-200429, filed Jul. 2, 2001, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention is directed to a valve timing control for a marine drive, and more particularly to an improved valve timing control for a marine drive that includes a variable valve timing mechanism.
2. Description of Related Art
A marine drive such as an outboard motor has a marine propulsion device powered by an engine. The propulsion device typically is a propeller and is submerged when an associated watercraft rests on a body of water. The outboard motor can employ either a two-cycle engine or a four-cycle engine. Recently, however, many outboard motors are offered with four-cycle engines because they provide better emissions control.
Typically, a four-cycle engine includes one or more intake and exhaust valves moving between an open position and a closed position. One or more camshafts can be provided to actuate the valves in a timed manner. When the intake valves are open, air is introduced into combustion chambers of the engine through the intake ports. When the exhaust valves are open, exhaust gases are discharged from the combustion chambers through the exhaust ports.
The engine typically includes one or more throttle valves to regulate an amount of air delivered to the combustion chambers. The throttle valves can be operated by the operator with a throttle lever. In general, the more the throttle valves open, the more power is output from the engine.
The engine can include a hydraulically operated variable valve timing (VVT) mechanism that can change opening and closing timing of the respective valves by changing an angular position of the camshaft or camshafts. A control device such as, for example, an electronic control unit (ECU) is used to control the VVT mechanism under various control strategies. For instance, the ECU controls the VVT mechanism either to set the valve timing at a fully advanced position for relatively high engine speeds to ensure high charging efficiency and high performance of the engine, or to set the valve timing at a fully retarded position for relatively low engine speeds to ensure high combustion efficiency, fuel economy and good emission control. Otherwise, the ECU controls the VVT mechanism to set the valve timing at a position between the fully advanced position and the fully retarded position in response to a running condition of the engine. Typically, the control by the ECU is a feedback control such that the ECU gives a target valve timing and controls the VVT mechanism to bring an actual valve timing close to the target valve timing.
Typically, the marine drive is provided with a transmission or transmission that changes a rotational direction of the propeller between forward, neutral or reverse. The transmission typically comprises a dog clutch and shift unit that operates the dog clutch. When in the forward and reverse positions, which are propulsion positions, the propeller propels the watercraft forward and backward, respectively. In the neutral position, which is a non-propulsion position, the propeller does not propel the watercraft because the propulsion shaft 226 is disconnected from the driveshaft.
When an engine is operating at idle speed with minimal load, it can exert considerable torque without movement of the throttle valve. For example, when a marine drive such as an outboard or inboard/outboard motor is at idle speed, the power output of the engine makes it difficult to move the transmission shift lever due to the load imparted to the transmission components. Additionally, when the transmission is shifted to a drive position, the engine is suddenly loaded and causes the propeller to begin to rotate almost instantaneously. The sudden movement of the propeller sends a shock through the drive train. This shock causes fatigue in the drive train and can make passengers in the associated watercraft feel uncomfortable. The shock is more severe and more noticeable when the marine drive is powered by a four-cycle engine.
One aspect of the present invention includes the realization that although variable valve timing mechanisms can be used to enhance the efficiency and thus increase the power output of internal combusion engines, they can also be used to reduce the power output of an engine. For example, in one mode, a VVT mechanism can be adjusted to an advanced intake valve timing during idle speed operation to reduce the power output and speed of the engine. As such, the load on the transmission can be reduced thereby allowing the transmission to be shifted more easily. Additionally, the reduced power output of the engine reduces the shock imparted to the drive train and the passengers of the associated watercraft.
Another aspect of the invention includes the realization that, under certain conditions, it is more beneficial to prevent adjustment of the valve timing. For example, sometimes a user may find it necessary or desirable to xe2x80x9cracexe2x80x9d the engine while the transmission is in the neutral position. In other words, a user may choose to actuate the throttle to increase the engine speed without causing the associated watercraft to move. A user might choose to race the engine in this manner to warm the engine more quickly, to un-foul a spark plug, to determine if a cylinder is mis-firing, or other reasons. Normally, the VVT mechanism would adjust the valve timing to follow a target timing when an engine is raced as such. However, if the valve timing is adjusted normally while the transmission is in neutral, the VVT mechanism may not be able to achieve a desired angular position immediately when the transmission is shifted into a drive position. Thus, a time lag can be generated causing the engine to temporarily operate in a compromised condition.
In accordance with one aspect of the present invention, a marine drive comprises an internal combustion engine. A propulsion device is powered by the engine. A transmission is arranged to switch the propulsion device between a propulsion position and a non-propulsion position. The engine comprises an engine body. A movable member is movable relative to the engine body. The engine body and the movable member together define a combustion chamber. The engine body defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an opening position and a closing position of the intake port. An exhaust valve is arranged to move between an opening position and a closing position of the exhaust port. A valve actuator is arranged to actuate either the intake valve or the exhaust valve. A change mechanism is arranged to change an actuating timing of the valve actuator at which the valve actuator actuates the intake valve or the exhaust valve. A control device is configured to control the change mechanism to set the actuating timing at a generally optimum timing. A sensor senses that the transmission is under operation and sending a signal to the control device. The control device controls the change mechanism based upon the signal to move the actuating timing away from the optimum timing.
In accordance with another aspect of the present invention, a marine drive comprises an internal combustion engine. A propulsion device is powered by the engine. A transmission is arranged to switch the propulsion device between a propulsion position and a non-propulsion position. The engine comprises an engine body. A movable member is movable relative to the engine body. The engine body and the movable member together define a combustion chamber. The engine body defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an opening position and a closing position of the intake port. An exhaust valve is arranged to move between an opening position and a closing position of the exhaust port. A valve actuator is arranged to actuate either the intake valve or the exhaust valve. A change mechanism is arranged to change an actuating timing of the valve actuator at which the valve actuator actuates the intake valve or the exhaust valve. A control device is configured to control the change mechanism to set the actuating timing at a generally optimum timing. A sensor is configured to sense whether the propulsion device is in the non-propulsion position and to send a signal to the control device. The control device is configured to control the change mechanism based upon the signal to adjust the actuating timing of the actuator toward a generally fully retarded or advanced timing.
A further aspect of the present invention is directed to a method for controlling a marine drive having a transmission configured to shift a propulsion device between a propulsion position and a non-propulsion position, an internal combustion engine including intake and exhaust valves, a valve actuator configured to actuate the intake and exhaust valves, and a change mechanism configured to change an actuating timing of the valve actuator at which the valve actuator actuates at least one of the intake valve and the exhaust valve. The method comprises setting the actuating timing at a first timing, determining whether the transmission is being shifted, and controlling the change mechanism to move the actuating timing away from the first timing when the determination is affirmative.
Yet another aspect of the invention is directed to a method for controlling a marine drive having a propulsion device, an internal combustion engine including intake and exhaust valves, a valve actuator configured to actuate the intake and exhaust valves, and a change mechanism configured to change an actuating timing of the valve actuator at which the valve actuator actuates at least one of the intake valve and the exhaust valve. The method comprises setting the actuating timing at a generally optimum timing, sensing whether the propulsion device is in a non-propulsion position, and controlling the change mechanism to bring the actuating timing to a generally fully retarded or advanced position when the determination is affirmative.
In accordance with another aspect of the invention, a marine drive comprises an internal combustion engine, a propulsion device powered by the engine, and a transmission configured to be shift the propulsion device between a neutral position and a drive position. The engine comprises an engine body, a movable member movable relative to the engine body, wherein the engine body and the movable member together defining a combustion chamber. The engine body also defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an open position and a closed position of the intake port. An exhaust valve is configured to move between an open position and a closed position of the exhaust port. A valve actuator is configured to actuate either the intake valve or the exhaust valve. Additionally, the engine includes means for changing an actuating timing of the valve actuator so as to reduce a load on the transmission while the transmission is being shifted.